Intranasal DNA Vaccine for Protection against Respiratory Infectious Diseases: The Delivery Perspectives

Xu, Yingying; Yuen, Pak-Wai; Lam, Jenny Ka-Wing

There are also several molecules being investigated to target APCs in general. One of the most widely studied molecules is the Flt3 ligand. Flt3 ligand is a growth factor that stimulates the proliferation of hematopoietic cells. It binds to the fms-like tyrosine kinase receptor Flt3. Flt3 expression is, in hematopoietic tissue, restricted to CD34 + progenitors, including DC progenitors. In vivo treatment of Flt3 ligand is found to up-regulate the number of DCs, but not their activation [125, 126] . Furthermore, Flt3 ligand treatment could also enhance immune response when delivered via the mucosal route [127] . It has been reported that when plasmid DNA encoding Flt3 ligand was co-administered with plasmids encoding protein antigens, effective immune responses were induced [128] . In addition to its APCs targeting ability, Flt3 ligand is an efficient and safe mucosal adjuvant that facilitated expansion of DCs following nasal administration [129, 130] .